Thermosetting protective coatings are widely used in original equipment manufacturer (OEM) and industrial maintenance fields. Binder resin options for these materials generally include polyester, epoxy, alkyd, and acrylic resins and can be formulated with different cross-linking materials. As the coatings industry faces stricter regulations with VOC emissions, waterborne versions of the binders used in such coatings which show good long-term stability and similar performance to their solvent-borne counterparts are of interest. Historically, there have been different approaches to achieving stable, solvent-free waterborne polyesters, but prolonged stability has been a challenge. In order to protect the polyester from hydrolysis in the presence of water, a stabilizing mechanism must be employed. In emulsion chemistry, other resin technologies have been successfully emulsified including alkyds, but traditional polyester resins that do not have fatty acid modification are more hydrophilic and thus make it problematic to identify a surfactant choice that has the proper interaction at the particle/water interface during inversion. Moreover, the level of surfactant must be at an acceptable level that does not impact the final film performance such as adhesion and water sensitivity. There are industry sectors trying to move towards lower volatile organic content (VOC) thermosetting coatings solutions. Thus, there exists a desire for the additional choice of a waterborne technology that can provide the balance of properties in a thermosetting coating application.
Surfactant choice for emulsification of polyesters must meet several criteria. For nonionic surfactants, the hydrophobia must show strong interaction capabilities with the polyester to enable dispersion in an aqueous continuous phase at elevated temperatures and maintain that interaction at room temperature. The surfactant must also be stable over the temperature range encountered during the emulsification process. Third, the surfactants must have cloud points sufficient to remain stable in the oil phase during the early stages of the emulsion process.
Such surfactants typically contain hydrophobes such as alkyl phenols, fatty acids, and fatty alcohols. These surfactants, though they show some interaction with conventional polyesters, have limitations on the stability of the emulsion over the desired emulsification temperature range. Thus, there exists a need to identify a surfactant class that provides aqueous polyester resins with an improved balance of stability and performance properties in a thermosetting coatings application.